A band gap reference (BGR) circuit (or a reference voltage generation circuit) may be used in a design of a semiconductor circuit, and may provide a constant voltage (a reference voltage). The reference voltage may be approximately 1.1V close to a band gap voltage difference of single crystalline silicon. In a semiconductor process, an operation temperature of a chip and an applied voltage may be changed.
A BGR circuit may have both an operating point where current may not flow in an internal current path and an operating point where current may flow. Since a BGR circuit may not perform an intended operation when current may not flow, a start-up circuit that may initially allow current to flow so as to reach an intended operating point may be necessary. Since a start-up circuit may continuously operate while allowing constant current to flow after start-up, it may be beneficial that current consumption of a start-up circuit may be minimized after start-up.
A current consumption of a start-up circuit may be changed according to a variation in an external power source, a variation in a device manufacturing process, and a temperature variation. According to a process, an external power source and a temperature may be adjusted. This may decrease a current consumption when a start-up circuit is designed such that the current consumption thereof may be significantly reduced. Hence, a start-up current may be excessively decreased. Thus, a start-up time of a BGR circuit may be increased or a BGR circuit may not start up.
In contrast, an external power source and a temperature may be adjusted to increase current consumption when a start-up circuit supplies sufficient current such that a BGR circuit may rapidly start up under temperature, voltage and process conditions with low current consumption, a current consumption of a start-up circuit may increase excessively. Therefore, it may be beneficial that a large current flows at a time of start-up. This may supply current necessary for start-up. Current consumed for operating a start-up circuit may be decreased after a start-up of a BGR circuit. This may decrease a power consumption of a semiconductor device. However, even after start-up, a related art start-up circuit may consume the same relatively high current as before start-up.
Hereinafter, an example of a related art start-up circuit for a BGR circuit will be described with reference to the accompanying drawings. FIG. 1 is a circuit diagram of a related art start-up circuit. It may include start-up circuit 10 and BGR circuit 12. Start-up circuit 10 may include transistors M1, M2, M4, M5, and M6. Since BGR circuit 12 may not change according to embodiments, an operation and a configuration of BGR circuit 12 will be described later with respect to embodiments. BGR, however, includes at least one transistor M0 and operational amplifier 14.
Referring to FIG. 1, since transistor M2 may have a diode structure in which a gate of transistor M2 may be connected to a drain thereof, current proportional to a forward voltage may flow. In a non-start-up state, transistors M0, M4, M5 and M6 may operate in a cut-off region. That is, current may not flow in BGR circuit 12. Therefore, gate voltage V(SRT) of transistor M1 may become a voltage obtained by subtracting a voltage across transistor M2 from supply voltage VDD. If supply voltage VDD is increased to about 1.5V or more, transistor M1 may turn on and a voltage VCONT may be decreased from supply voltage VDD. If voltage VCONT is decreased to a voltage lower than supply voltage VDD, transistors M0, M4, M5 and M6 may turn on and current proportional to current Ibgr may flow in start-up circuit 10.
Transistors M0, M4, M5 and M6 may be configured as a current mirror structure. At this time, if a driving current of transistor M4 becomes larger than current Irefstart supplied from transistor M2, voltage V(SRT) may be decreased and may be close to a reference voltage, for example, ground voltage (GND). Transistor M1 may be introduced into a cut-off region again. If transistor M1 is turned off, voltage VCONT may be controlled only by operational amplifier 14.
An operating point of BGR circuit 12 may be checked by changing and comparing current Irefstart flowing in transistor M2 and BGR current Ibgr flowing in transistor M0 with a predetermined ratio. At this time, a current flowing in transistor M2 may be changed according to various conditions such as a manufacturing process, temperature, supply voltage VDD, and voltage V(SRT). Since transistor M2 may have a diode structure and a current flowing in transistor M2 may be increased in proportion to a second power of a voltage across transistor M2, a variation width of current Irefstart may be significantly increased if a range of supply voltage VDD used is wide. Since voltage V(SRT) may become zero after start-up, current Irefstart may further increase as compared with before start-up and may thus continuously flow. Although a resistor may be used to reduce a dependency on supply voltage VDD, this method may not be desirable because a relatively large space may be required as compared with a transistor.